In the handling of molten aluminum and its alloys, it is highly desirable to utilize refractory products per se, or refractory lined parts having low thermal conductivity, which are chemically inert to the molten metal. These products, for example, may take the form of pressed boards used for baffles or the lining launder systems, or tubular members through which the molten metal may be poured during transfer process.
The machineability of these products is important as machining in the aluminum industry is generally accomplished using standard wood working machines and techniques. Since a wide variety of shapes are utilized, it is more economical to machine parts than to order sized components. Typical applications may require cutting, drilling, tapping, trepanning, thread grinding or milling, sanding, the use of forming tools such as lathes to form curved surfaces or those of stepped, angular or irregular shape, or techniques which otherwise produce an edge which must be retained in service. For example, a continuous thread may be turned on a tubular member.
Materials have been used in the past which also possessed other desirable properties for success in molten aluminum application such as dimensional stability, spall resistance, and resistance to thermal and mechanical shock. Fibrous refractories, such as are disclosed in U.S. Pat. Nos. 3,269,849 and 3,294,562, are known to have particular utility in this regard. However, such refractories contain predominant amounts of asbestos fibers, and asbestos has now been linked to as a cause of at least three major diseases--asbestosis, lung cancer and mesothelioma. Due to the fact that many aluminum shops have become accustomed to working with wood working machines and techniques which may generate atmospheric contaminants, it has become highly undesirable to utilize refractories having asbestos fibers. Many fibrous refractory compositions, however, can not be used in lieu of asbestos fiber systems since, in application, the fibers or the composition would either disintegrate or have insufficient heat resistance, or otherwise not exhibit the desired properties described above with respect to molten aluminum exposure.
Thus, there exists a need for a suitable substitute for the asbestos refractory products which is amenable to the maching operations described while having characteristic properties similar to those of the previously used asbestos fibrous refractories.